M. Orlandi et al. / Tetrahedron 57 (2001) 371±378
377
Further puri®cation by preparative HPLC (isocratic gradient
CH3CN±H2O 1:1) yielded analytically pure phenyl-
coumaran 6: (0.44 g, 56% yield), mp 2058C; H NMR:
0.02 M phosphate/citric acid buffer (4.0 mL, pH 3.5) was
cooled to 08C. 0.86 M Aqueous hydrogen peroxide
(0.60 mL, 0.5 mmol) and aqueous HRP (0.93 mL, 837 U)
were added to the reaction vessel in small portions over
15 min. The mixture was stirred at 08C for 4 h, and saturated
aqueous NaCl (20 mL) was added. Acetone was removed by
rotary evaporation, and the resulting solution was extracted
with AcOEt (4£20 mL). The combined organic extracts
were washed with 5% aqueous NaHCO3 (25 mL), water
(25 mL), and dried over Na2SO4. The solvent was evapo-
rated under reduced pressure, and the residue was puri®ed
by silica gel ¯ash cromatography with toluene±AcOEt
(gradient mode, from 4:1 to 1:1) yielding a mixture of
phenylcoumarans 14 and 15 (156 mg, 40%) with 1:9 ratio.
The minor diastereomer 14 and the major one 15 were then
separated by preparative HPLC (isocratic mode, CH3CN±
1
7.58 (d, J15.0 Hz, 1H), 6.35 (d, J8.0 Hz, 1H), 6.31 (d,
J15.0 Hz, 1H), 6.12 (d, J8.0 Hz, 1H), 5.95 (d, J7 Hz,
1H), 5.60 (s, 1H), 4.71 (dq, J7.0, 8.0 Hz, 1H), 4.60 (dq,
J7.0, 8.0 Hz, 1H), 4.30 (q, J8.0 Hz, 2H), 4.30 (q,
J8.0 Hz, 2H), 3.95 (s, 3H), 3.90 (s, 3H) 1.45 (d,
J7.0 Hz, 3H), 1.40, (d, J7.0 Hz, 3H), 1.25 (t,
J8.0 Hz, 3H),1.20 (t, J8.0 Hz, 3H); MS (EI) m/z 584
(M1) (100), 495 (20), 481 (20); IR (nujol): 3200, 1462
(cm21); Anal. Calcd for C30H36O10N2: C, 61.64; H, 6.16;
N, 4.79. Found: C, 61.68; H, 6.19; N, 4.75. [a]2D5148.3
(AcOEt, c 0.1).
4.2. Hydrolysis of major phenylcoumaran 6 and esteri-
®cation of the diacid 7
1
H2O 1:1) yielding pure 15 (140 mg, 36% yield). H NMR:
7.73 (d, J15.0 Hz,1H), 6.88±7.19 (m, 5H), 6.10 (d,
J8.0 Hz, 1H), 5.90 (s, 1H), 5.80 (d, J8.0 Hz, 1H), 4.20
(d, J8.0 Hz, 1H), 4.00 (dd, J5.5, 7.0 Hz), 3.99 (dd,
J5.5, 7.0 Hz), 3.92 (s, 3.0), 3.85 (s, 3.0), 3.60 (d,
J4.0 Hz, 2H), 3.51 (d, J4.0 Hz, 2H), 2.15±2.20 (m,
4H), 1.85±1.96 (m, 6H), 1.25±1.45 (m, 6H), 1.30 (s, 3H),
1.21 (s, 3H), 0.99 (s, 3H), 0.80 (s, 3H); MS (FAB1) m/z 781
(M11)1 (10), 564 (20), 536 (20), 351 (100). Anal. Calcd for
C40H48O10N2S2: C, 61.54; H, 6.15; N, 3.59. Found: C, 61.60;
H, 6.20; N, 3.50. The minor diastereoisomer 14 was not
characterized.
Phenylcoumaran 6 (0.10 g, 0.24 mmol) was dissolved in
THF (20 mL), and aqueous 10 M hydrogen peroxide
(1.0 mL, 10.0 mmol) was added. LiOH (70 mg, 2.4 mmol)
in water (3 mL) was added over 10 min under stirring. After
18 h at room temperature the reaction mixture was ice-
cooled, then saturated aqueous sodium bisul®te was added
dropwise until a negative response was observed with
starch-iodide paper. THF was removed by rotary evapora-
tion, and aqueous 0.1 M HCl was added dropwise to pH 5.
The aqueous mixture was extracted with ethyl acetate
(3£30 mL), and the combined organic extract were washed
with water (25 mL) and dried over Na2SO4. The solvent was
evaporated under reduced pressure affording crude 7, which
was dissolved in 40 mL of saturated ethereal diazomethane.
The solvent was removed and the residue was puri®ed by
preparative HPLC (isocratic CH3CN±H2O 1:1) giving
analytically pure (2)-trans-(2S,3S)-dehydrodiferulate 8
(10 mg, 10% yield), [a]2D5274.0 (CHCl3, c 0.2).
4.5. Ag2O Promoted oxidative phenol coupling of
compound 13
A solution of 13 (0.20 g, 0.5 mmol) in dry CH2Cl2 (5.0 mL)
was added with silver(I)oxide (0.18 g, 0.8 mmol) under
argon atmosphere at room temperature. After stirring for
24 h, the mixture was ®ltered through a Celite pad and
evaporated under reduced pressure. The residue was puri-
®ed by silica gel ¯ash chromatography with toluene±AcOEt
(gradient mode, from 4:1 to 1:1) yielding a mixture of
phenylcoumarans 14 and 15 (62 mg, 35%) with 1:12 ratio.
The minor diastereomer 14 and the major one 15 were
separated by preparative HPLC (isocratic mode, CH3CN±
H2O 1:1) yielding pure phenylcoumaran 15 (57 mg, 32%
yield). The minor diastereoisomer 14 was not characterized.
4.3. Preparation of camphor sultam derivative 13
NaH (37 mg 1.54 mmol) was suspended in toluene (50 mL)
and 11 (0.30 g, 1.4 mmol) was added under magnetic stir-
ring. After 30 min, 4-acetylferulic acid chloride 1042
(0.39 g, 1.7 mmol) was added, and the mixture was stirred
for 2 h at room temperature. The organic layer was washed
with water (20 mL), dried over Na2SO4 and evaporated. The
residue was dissolved in CH3OH (8 mL), and 1 M CH3ONa
in CH3OH (0.75 mL, 0.75 mmol) was added. The mixture
was stirred for 30 min; water (5 mL) was added, the organic
layer was dried over Na2SO4 and evaporated affording crude
13. Silica gel ¯ash chromatography of the residue (isocratic;
4.6. Reduction of major phenylcoumaran 8
trans-(2S,3S)-Dehydrodiferulate 8 (10 mg, 0.024 mmol)
was dissolved in dry THF (5 mL) under argon at 2788C.
LiBH4 (1 mg, 0.054 mmol) was suspended in dry THF
(1.0 mL) and added to the reaction mixture, which was
further stirred for 2 h at 2788C. 80% Aqueous THF
(10 mL) was added slowly, and aqueous 0.1 M ammonium
chloride (5 ml) was then added. The mixture was extracted
with AcOEt (2£10 mL), and the combined organic extracts
were washed with water (10 mL) and then dried over
Na2SO4. The solvent was evaporated under reduced pres-
sure, and the residue was analysed by HPLC with a chiral
column (Chiralcell OF; isocratic mode, hexane±isopropanol
1:1) in comparison with authentical specimens of both
enantiomers of dehydrodiconiferyl alcohol.36 The major
diastereoisomer is trans-(2S,3R)-(1)-dehydrodiconiferyl
alcohol.43,44
1
hexane±AcOEt 1:1) gave pure 13 (0.52 g, 85% yield). H
NMR 7.73 (d, J15.0 Hz, 1H), 6.88±7.19 (m, 4H), 5.89 (s,
1H), 3.99 (dd, J5.5, 7.0 Hz), 3.92 (s, 3.0), 3.51 (d,
J4.0 Hz, 2H), 2.15±2.20 (m, 2H), 1.85±1.96 (m, 3H),
1.25±1.45 (m, 3.0), 1.21 (s, 3.0), 0.99 (s, 3.0). MS of 12
(EI) m/z 433 (M1) (10), 391, (65), 177 (100). [a]2D5163.0
c 0.043); HREIMS of 12 calculated for
(CHCl3,
C22H27O6NS: 433.1559; found 433.1573.
4.4. Horseradish Peroxidase (HRP) promoted oxidative
phenol coupling of compound 13
A solution of 13 (0.40 g, 1.0 mmol) in acetone (14 mL) and